4.5 KETONES

Question 1

What are the three intermediate products of fat metabolism classified as ketones?

Answer 1

Acetone (2%),
acetoacetic acid (20%), and
β-hydroxybutyrate (78%)

Question 2

Why are measurable amounts of ketones typically absent in urine?

Answer 2

Fat metabolism is usually complete, breaking down fat into carbon dioxide and water.

Question 3

When do ketones appear in urine?

Answer 3

When carbohydrate metabolism is compromised, requiring fat metabolism for energy

Question 4

What are common clinical causes of increased fat metabolism leading to ketonuria?

Answer 4

Diabetes mellitus,
starvation,
vomiting, and
malabsorption

Question 5

Why is testing for ketones important in type 1 diabetes mellitus?

Answer 5

It helps monitor insulin dosage and indicates insulin deficiency.

Question 6

What serious complications can result from increased ketones in the blood?

Answer 6

Electrolyte imbalance,
dehydration,
acidosis, and
diabetic coma.

Question 7

Besides diabetes, what conditions can produce ketonuria?

Answer 7

Starvation,
strenuous exercise,
alcoholism,
febrile states in children, and
cold exposure.

Question 8

What reagent is used in the ketone strip test?

Answer 8

Sodium nitroprusside

Question 9

Which ketone does the sodium nitroprusside reaction primarily detect?

Answer 9

Acetoacetic acid

Question 10

How are ketone test results on reagent strips reported?

Answer 10

Qualitatively (negative, trace, small, moderate, large) or semiquantitatively (5–160 mg/dL)

Question 11

What substances can cause false-positive ketone results?

Answer 11

Levodopa,
phthalein dyes,
highly pigmented red urine, and
medications with sulfhydryl groups.

Question 12

What can cause false-negative ketone results

Answer 12

Improper specimen preservation,
glucose interference, and
volatile loss of acetone.

Question 13

What is the purpose of glycine in some ketone reagent strips?

Answer 13

To enhance sensitivity to acetone detection.

Question 14

What is the principle of the Acetest tablet test for ketones?

Answer 14

It uses sodium nitroprusside with glycine and lactose for better color differentiation.

Question 15

It uses sodium nitroprusside with glycine and lactose for better color differentiation.

Answer 15

Automated methods now measure β-hydroxybutyrate more accurately.

Question 16

What are the key reagents in the Acetest tablets?

Answer 16

Sodium nitroprusside, glycine, disodium phosphate, and lactose.

Question 17

How does improper specimen preservation affect ketone test results?

Answer 17

It allows acetone volatilization and bacterial breakdown of acetoacetic acid, leading to false negatives.

Question 18

Which ketone is most concentrated in urine, but not directly detected by the reagent strip

Answer 18

β-hydroxybutyrate

Question 19

What conditions correlate with ketonuria?

Answer 19

Diabetic acidosis,
starvation,
malabsorption,
vomiting,
cold exposure,
strenuous exercise, and
febrile states in children.

Question 20

How does strenuous exercise lead to ketonuria?

Answer 20

overusing available carbohydrates, resulting in increased fat metabolism.

Question 21

What is the role of lactose in Acetest tablets?

Answer 21

It improves color differentiation during the test.

Question 22

What is the main ketone body in blood and urine that is not directly detected by routine ketone reagent strips?

Answer 22

β-hydroxybutyrate

Question 23

What percentage of each ketone is typically found in the body during ketosis?

Answer 23

hydroxybutyrate (78%), acetoacetic acid (20%), and acetone (2%).

Question 24

What is the primary reaction in the ketone reagent strip test?

Answer 24

The sodium nitroprusside reaction in an alkaline medium.

Question 25

What does a positive ketone test indicate in weight-loss clinics?

Answer 25

Avoidance of carbohydrates and increased fat metabolism

Question 26

Why are reagent strip tests not equally sensitive to all ketones?

Answer 26

They primarily measure acetoacetic acid and are only slightly sensitive to acetone when glycine is present.

Question 27

How can vomiting lead to ketonuria?

Answer 27

By causing a loss of carbohydrates and forcing the body to metabolize fat for energy.

Question 28

What are the potential adverse effects of prolonged ketonuria on the kidneys?

Answer 28

Toxicity to kidney tubules

Question 29

How are ketones formed in the body?

Answer 29

Acetoacetic acid is the precursor for both β-hydroxybutyrate and acetone.

Question 30

What practical application does ketone testing have in patients undergoing frequent strenuous exercise?

Answer 30

Monitoring for overuse of carbohydrates and potential kidney stress

Question 31

What clinical significance does ketonuria have in febrile children?

Answer 31

It may indicate accelerated metabolism and inadequate carbohydrate availability.

Question 32

What happens to acetoacetic acid and acetone in improperly preserved specimens

Answer 32

Acetoacetic acid breaks down, and acetone volatilizes, causing false-negative results.

Question 33

How can modern automated methods improve ketone testing

Answer 33

By directly measuring β-hydroxybutyrate levels in serum and body fluids

Question 34

What additional role does the Acetest tablet test serve besides confirming urine ketones?

Answer 34

It is used for testing ketones in serum and other body fluids during severe ketosis.

Question 35

Why is proper timing essential in interpreting ketone reagent strip tests?

Answer 35

Delayed readings can cause false-positive results due to atypical color reactions.

Question 36

What specific substances in improperly preserved specimens interfere with ketone detection?

Answer 36

Bacteria and volatile acetone compounds

Question 37

Why might ketonuria be detected in individuals with alcoholism?

Answer 37

Alcohol metabolism can deplete carbohydrates, requiring fat metabolism

Question 38

What key metabolic changes lead to diabetic acidosis?

Answer 38

Accumulation of ketones in the blood due to insulin deficiency.